In motion picture projectors, a succession of transparent or semi-transparent still images or frames are sequentially advanced before a suitable light source, thereby projecting an image onto a projection surface. The film is moved or advanced until a frame is in alignment with the projection aperture and then held stationary for a discrete period of time during which light is passed during two discrete time periods through the aperture, film frame, and then a focusing lens, resulting in an image being projected onto a screen. This is followed by movement of the film until the next frame is in alignment with the projection aperture. The rapid sequential advancement of the individual still frames, typically on the order of 24 frames per second, produces the illusion of motion. Typically, the film disposes at least one soundtrack synchronized with the picture projection. In this regard, recent advances in analog and digital sound recording technology have been rapidly incorporated in to modern films and film projector sound systems, more commonly referred to as xe2x80x9csound headsxe2x80x9d.
To effectuate sequential film advancement, motion picture projectors utilize toothed drive sprockets connected to a motor driven xe2x80x9cstar wheelxe2x80x9d to sequentially pull a length of film before the light source. Such motion picture projectors further include tensioning shoes for maintaining the filmstrip in contact with the drive sprockets. The film disposes two drive tracks which are engaged by the toothed sprockets, thereby enabling frame advancement. Motion picture filmstrips generally include at least one soundtrack positioned near the edge of the film or within at least one film drive track.
Commonly, motion picture projectors utilize a film trap and gate assembly to precisely align and position a filmstrip within an illumination plane. The film trap and gate assembly includes a pair of runners which provide controlled movement of the filmstrip past an illumination aperture. The edges of the filmstrip contact the runners, pressure bands, and tensioning shoes during operation. Consequently, over a period of time the edges of the filmstrip may become scratched or damaged due to the film remaining in constant contact with the runners, pressure bands, and tensioning shoes. Additionally, foreign materials such as dust, residues, and other impurities located on the runners, pressure bands, or tensioning shoes may be deposited on the film. The damage to the edges of the filmstrip or the foreign material deposited on the film may prevent the soundtracks from being clearly reproduced by the sound head.
Additionally, motion picture projectors are designed primarily for forward film advancement, in that the drive sprockets pull the filmstrip past an illumination aperture. On occasion, a film trap will include a sharpen device called a stripper plate located near the drive sprocket, to strip film splices when the film is moved through the projector in reverse. Pushing a flexible portion of film material past the sharpened stripper plate and past the runners, pressure bands, and tensioning shoes is often impossible. Moreover, severe damage to a filmstrip could occur should the filmstrip contact the stripper plate. As such, reversing the direction of the film, particularly while viewing, often results in damage to the film.
Thus, there is a need for a film trap and gate assembly for a motion picture projectors which reduces the amount of surface wear on the edges of the filmstrip, thereby increasing the lifetime of each film print. There is a further need for a film trap and gate assembly which enables the operator to reverse the direction of film travel without damaging the film.
The present invention solves the need for a film trap and gate assembly which reduces the damage to a filmstrip disposed therein, thereby extending the usable lifetime of the motion picture. The film trap and gate assembly disclosed herein has eliminated the need for maintaining constant contact between the film and the spring-loaded runners, pressure bands, and steel tensioning shoes thereby reducing or eliminating any damage to the filmstrip. Additionally, the present invention permits an operator to reverse the direction of film movement through the projector, while viewing or at higher speed, without damaging the film. The present invention may be utilized on a en number of film projector systems with little or no modification required.
The film trap and gate assembly of the present invention comprises a film movement channel, which defines a discreet area which the film strip may traverse. The film movement channel, which is formed by the film gate engaging the film trap, forms and orifice larger than the thickness of the film disposed therein. Similarly, the width of the film movement channel is greater than the width of the film positioned therein. Unlike prior art systems, which utilized spring-loaded pressure bands located on the film trap which remain in constant contact with the film and forcibly bias the film against the film gate, the film movement channel of the present invention permits a degree of film movement or float within the channel. As a result, damage to the film has been reduced or eliminated while the usable lifetime of the filmstrip has been increased.
In an additional embodiment, the present invention discloses a film trap comprising a trap body having image aperture formed therein, and having a first and second trap rail assembly positioned thereon. The first trap rail assembly comprises a first trap rail in communication with a first trap guide. Similarly, the second trap rail assembly comprises a second trap rail in communication with a second trap guide. The film is positioned on the first and second trap rails. The amount of lateral displacement the film is limited by the first and second trap guides. Those skilled in the art will appreciate the present invention has eliminated the need for constant pressure applied by the spring-loaded pressure bands the film, thereby decreasing or eliminating damage to the film during operation.
Additionally, the present invention discloses a film tensioning device which is attachable to a film gate. The film tensioning device comprises a deformable body having at least tensioning roller attached thereto, and a tensioning device in communication with tensioning rollers. The deformable body may further comprise a roller cradle which positions the tensioning rollers on the deformable body. Those skilled in the art will appreciate the tensioning rollers of the present invention may be comprised of non-abrasive materials, including, without limitation, elastomers, urethanes, and rubbers. In another embodiment, the tensioning device may be actuated to adjust the tensioning force applied by the tensioning rollers.
In yet another embodiment of the present invention a film trap and gate system is disclosed herein. The film trap and gate system comprises a film trap capable of engaging a film gate. The film trap comprises a trap body having an image aperture formed thereon, and a first and second rail assembly attached thereto. The film trap further disposes a stripper plate comprising an angled stripper blade in communication with an attachment flange. The stripper plate is attached to the attachment flange at an at least one degree angle, thereby enabling the movement of the film to be reversed. The film gate comprises a gate body having a projection aperture formed therein, and a first and second rail assembly attached thereto. A film tensioning device is attached to the gate body. The tensioning device comprises a deformable body having an attachment orifice formed therein, an a roller cradle attached thereto. The attachment orifice preferably forms an attachment slot thereby enabling the user to adjust the length of the film tensioning device with respect to the gate body. At least tensioning rollers are in communication with the roller cradle. A tensioning device is in communication with the roller cradle such that the tensioning force applied by the tensioning device may be adjusted by the user.
In an alternate embodiment, the present invention discloses a film gate stripper plate for use in motion picture projectors. The stripper plate comprises a stripper blade attached to an attachment flange. The stripper plate is angled, preferably towards the gate body, at least one degree. Those skilled in the art will appreciate the present invention permits the movement of the film to be reversed without the film contacting the stripper blade, thereby reducing the likelihood of damaging the film.
In another embodiment, the present invention discloses a film trap and gate calibration device comprising a first member and a second member. The first member has a thickness greater than the thickness and width larger than motion picture film. The second member has a thickness and width smaller than the thickness of motion picture film. The operator may then position the trap and gate rails to be calibrated to be slightly larger or smaller than the motion picture film disposed thereon.
The present invention discloses a method of advancing motion picture film through a motion picture projector. The advancement method comprises locating film within a film projector, using the a film trap and gate assembly to form a film movement channel within the projector, positioning the film within the film movement channel, attaching the film to a film drive system, and moving the film through the film advancing channel. Those skilled in the art will appreciate the present method results in the film intermittently contacting the film trap, film gate, or both, rather than utilizing constant pressure commonly used in prior art system.
Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings.